(i) Field of the Invention
The present invention relates to polymer granules having a specific outer surface shape collected from a solvent solution of a polymer, and a process for preparing the same. More specifically, it relates to spherical polymer granules having a specific outer surface shape and containing a less remaining solvent, particularly polycarbonate granules and a process for preparing the same.
(ii) Description of the Related Art
As means for collecting a solid polymer from its organic solvent solution, various techniques have been suggested and put to practical use. In particular, a polycarbonate is usually manufactured by an interfacial polycondensation method, and then often collected as a solid polycarbonate in-the form of fine particles, granules formed by the gathering of these fine particles or the like from its organic solvent solution. Most of the various methods for collecting the solid polycarbonate which have heretofore been proposed require specific devices, and so there has not been developed a method for isolating and collecting the solid polycarbonate at a low cost without using the expensive devices. For example, as methods for collecting the above-mentioned polymer, there have been known a method which comprises only adding a poor solvent to a polymer solution (Japanese Patent Publication No. 14474/1967), a method which comprises pulverizing the polymer by a kneader (Japanese Patent Publication No. 15899/1978) and a method which comprises pouring the polymer into warm water, and then pulverizing it (Japanese Patent Application Laid-open No. 74231/1989). However, these methods all require specific facilities, which increases the cost of the facilities and the polymer collection inconveniently.
On the other hand, when the polymer is collected from the organic solvent solution of the polymer, particularly the polycarbonate, a large amount of the solvent usually remains in the solid polymer, and this fact deteriorates the quality and physical properties of a polymer product such as the polycarbonate. In order to solve this problem, various techniques have been disclosed. For example, there has been a method which comprises feeding a polymer solution to the polycarbonate granules to vaporize a solvent (Japanese Patent Application laid-open Nos. 189835/1992 and 226541/1992), but in this method, a dense polycarbonate powder is formed, so that drying characteristics are very poor. If the powder is heated up to about 250.degree. C. so as to improve the drying characteristics, the polymer particles are inconveniently liable to fuse and deteriorate, and the particle diameter of the particles obtained by the continuous operation of this method is merely large, which makes the industrial continuous operation essentially impossible.
In addition, an improved technique of this method has been present in which a poor solvent is poured into a polymer solvent solution, followed by the above-mentioned operation (Japanese Patent Application Laid-open No. 17586/1993). However, also for the particles obtained by the improved technique, it is inconveniently necessary to dry them for a long period of time.